DIFFERENTIAL ACTIVATION AND CONSERVED VEGETATIVE CELL-SPECIFIC ACTIVITY OF A LATE POLLEN PROMOTER IN SPECIES WITH BICELLULAR AND TRICELLULAR POLLEN

The activation and developmental regulation of the promoter of the tom ato tate pollen gene lat52 was analysed in Nicotiana fabacum and Arabi dopsis thaliana to investigate the conservation of regulatory mechanis ms in species with bicellular and tricellular pollen. Promoter activit y in transgenic plants containing the lat52 promoter fused to the beta -glucuronidase (gus) gene was studied in detail throughout pollen deve lopment by fluorimetric and histochemical analysis of GUS activity, an d by RNA analysis. These studies showed that in transgenic A. thaliana the lat52 promoter was activated in late uninucleate microspores imme diately prior to microspore mitosis, whereas in transgenic N. tabacum lat52 promoter activity was first detectable immediately following mic rospore mitosis in young bicellular pollen grains. Thus, the precise a ctivation of the lat52 promoter was not strictly dependent on passage through microspore mitosis in A. thaliana. Despite this temporal diffe rence, the pattern of lat52 promoter activity during vegetative cell m aturation showed a very similar cumulative pattern of activity in both species, which was correlated with a similar accumulation of gus tran script and spore protein content. Furthermore, the expression of a lat 52 promoter directed nuclear-targeted beta-glucuronidase fusion protei n allowed lat52 promoter activity to be localized specifically to the vegetative cell during pollen development in A. thaliana.